1. Field of Invention
This invention relates to RF stand offs or breaks and in particular, but not exclusively, to stand offs, which are suitable for use in plasma generating apparatus.
2. Background of the Invention
In RF plasma vacuum processing equipment, it is often necessary to provide a gas feed to a live RF part. For example, helium may be required for backside cooling of an RF driven wafer chuck or a process gas may need to be fed to an RF driven showerhead. In the latter case, the gasses used may only be gaseous at elevated temperature and this means that the gas lines require heating throughout the gas delivery system including, ideally, any insulating or resistive pipe work used as part of an RF stand off.
The problems that can occur in controlling the RF Field strength in the gas feed and trying to ensure the RF voltage is evenly dropped along its length are discussed in U.S. Pat. No. 5,725,675, which uses a resistive potential divider approach to ensure even dropping of the RF voltage.
However, the solutions discussed do not provide for directed heating of the insulating or resistive gas feed and this is because, until now, it has been thought necessary to use bulky and costly RF blocking inductors to prevent RF being picked up by either or both the heating element or thermocouple and being fed back to heater power supplies and control electronics with potentially damaging consequences. Indirect heating, for example hot air blowing, has been considered, but in many cases is not practical.